Systems such as automotive, aviation, telecommunications, consumer electronics, etc. comprise many elements that may be adversely affected by physical, environmental, and electrical stresses. These elements include electronic components, passive circuit elements, and interconnect structures. One type of stress that interferes with the proper operation of an electrical system is electromagnetic radiation. This type of stress is also referred to as Electromagnetic Interference (“EMI”). In addition to being affected by EMI, the electronic components also radiate electromagnetic signals, which may adversely affect other circuit components either in the same system or in other systems. As the desire for smaller more compact systems has increased, systems manufacturers have decreased the sizes of their systems, which increases the likelihood that radiated EMI will affect the system. For example, switched mode power supplies (“SMPS's”), which are used in portable computers, hand-held devices such as cellular phones, personal digital assistants, and electronic games, among others, are typically one of the worst sources of EMI. Because the sizes modern electronic systems have decreased, components that are sensitive to EMI may be located in close proximity to the power supplies thereby increasing their probability of malfunction due to the EMI.
Passive techniques for mitigating the effects of radiated EMI in electronic systems comprising SMPS's have included the use of EMI snubbers. However, snubbers are expensive and increase the size of the electronic system. Active techniques for addressing radiated and conducted EMI rely on varying the switching frequency of the SMPS. These techniques include the use of pseudo random clocks, frequency-modulated clocks, chaotic peak current control, and delta sigma modulation to achieve variable frequency operation. By varying the switching frequency, the noise generated by the SMPS is spread in the frequency domain and the fundamental peak is significantly reduced. A drawback with these techniques is that they have only been realizable in analog feedback controllers.
Hence, a need exists for a circuit and method that mitigates the effects of radiated and conducted EMI that can be applied to SMPS's having digital feedback controllers. In addition, it is desirable for the circuit and method to be cost and power efficient.